Question

Consider the hypothetical situation where the azimuthal quantum number, $\mathrm{l}$, takes values $0$, $1$, $2$, ...... $n+1$, where $\mathrm{n}$ is the principal quantum number. Then, the element with atomic number:

• A. $13$ has a half-filled valence subshell.
• B. $9$ is the first alkali metal.
• C. $8$ is the first noble gas.
• D. $6$ has a $2p$- valence subshell.

Answer 1

The correct option is A

$13$ has a half-filled valence subshell.

Explanation for correct option:

A. $\mathbf{13}$ has a half-filled valence subshell

1. As atomic numbers are given, from which we can derive electronic configuration for the given atomic number.
2. ${}_{13}\mathrm{X}=1{\mathrm{s}}^{2}1{\mathrm{p}}^{6}1{\mathrm{d}}^5$ here we can observe that the d-block is half-filled.
3. So, the element with an atomic number $13$ has a half-filled valence subshell.

Explanation for incorrect option:

B. $\mathbf{9}$ is the first alkali metal

1. ${}_9\mathrm{X}=1{\mathrm{s}}^{2}1{\mathrm{p}}^{6}1{\mathrm{d}}^1$here we can observe that the valence shell is d hence the given metal is a d-block element.
2. So, the element with atomic number $9$ is not alkali metal as alkali metals are s-block elements.

C. $\mathbf{8}$ is the first noble gas

1. ${}_8\mathrm{X}=1{\mathrm{s}}^{2}1{\mathrm{p}}^6$ here we can observe that the element with a full-filled p-subshell is the second noble gas.
2. First noble gas has a full-filled s-subshell i.e $1{\mathrm{s}}^2$.

D. $\mathbf{6}$ has a $\mathbf{2}\mathit{p}$- valence subshell

1. ${}_6\mathrm{X}=1{\mathrm{s}}^{2}1{\mathrm{p}}^4$ here we can observe that the in element with atomic number $6$ we have $1\mathrm{p}$ subshell.
2. So, no $2\mathrm{p}$ valence subshell is present in

Hence option A is correct, $13$ has a half-filled valence subshell.